1. Field of the Invention
The present invention relates generally to embryonic stems cells, and more specifically to a process for obtaining human embryonic stem cells using parthenogenically activated oocytes.
2. Background Information
Human embryonic stem cells (ES) cells are pluripotent cells that can differentiate into a large array of cell types. When injected into immune-deficient mice, embryonic stem cells form differentiated tumors (teratomas). However, embryonic stem cells that are induced in vitro to form embryoid bodies (EBs) provide a source of embryonic stem cell lines that are amenable to differentiation into multiple cell types characteristic of several tissues under certain growth conditions. For example, ES cells become differentiated into neurons in the presence of nerve growth factor and retinoic acid.
Human ES cells and their differentiated progeny are important sources of normal human cells for therapeutic transplantation and for drug testing and development. Required by both of these goals is the provision of sufficient cells that are differentiated into tissue types suitable for a patient's needs or the appropriate pharmacological test. Associated with this is a need for an efficient and reliable method of producing differentiated cells from embryonic stem cells.
Currently, human embryonic stem cells (hES) are derived from three sources: blastocysts remaining after infertility treatments and donated for research, blastocysts generated from donated gametes (oocytes and sperm), and the products of nuclear transfer (NT). Cadaveric fetal tissue is the only source of human embryonic germ cells (hEG). hES and hEG cells offer remarkable scientific and therapeutic possibilities, involving potential for generating more specialized cells or tissues. Ethical concerns about the sources of hES and hEG cells, however, and fears that use of NT for research could lead to use of NT to produce a human being, have fostered a great deal of public discussion and debate.
Parthenogenic activation of mammalian oocytes may be used as an alternative to fertilization by sperm/NT to prepare oocytes for embryonic stem cell generation. Parthenogenic activation is the production of embryonic cells, with or without eventual development into an adult, from a female gamete in the absence of any contribution from a male gamete.
Parthenogenetic activation of mammalian oocytes has been induced in a number of ways. Using an electrical stimulus to induce activation is of particular interest because electrofusion is part of the current nuclear transfer procedure. Parthenogenetic activation in vitro by electrical stimulation with electrofusion apparatus used for embryonic cell-oocyte membrane fusion has been reported.
Mouse oocytes have been activated by exposure to Ca+2—Mg+2 free medium, medium containing hyaluronidase, exposure to ethanol, Ca+2 ionophores or chelators, inhibitors of protein synthesis, and electrical stimulation. These procedures have led to high rates of parthenogenic activation and development of mouse oocytes, but did not activate and/or lead to a lower development rate of young bovine oocytes. Further, fertilization and parthenogenic activation of mouse oocytes is also dependent on post ovulatory aging.
Activation of bovine oocytes has been reported by ethanol, electrical stimulation, exposure to room temperature, and a combination of electrical stimulation and protein inhibition with cycloheximide. While these processes are thought to raise intracellular Ca+2, they are most successful when the oocytes have been aged for more than 28 hours.